I really don't like to rate people by apperance, but I want to answer your question.
For teenage stars, I'd pick Selena Gomez because I adore her beautiful hair and smile.
For adult stars, I'd say Britney Spears because I love her teeth (smile), eyes and hair. And I've just always loved Jennifer Aniston's apperance, I've always thought she was so pretty. So I'm picking Britney Spears and Jennifer Aniston for adult stars, one singer and one actress.